Remove 'Script' string in programs names

Script_rename_contigs_genes.py -> Rename_contigs_and_genes.py

Script_barplot_kaiju.py -> Generate_barplot_kaiju.py

Script_filter_cpm_contigs.py -> Filter_contig_per_cpm.py

Script_quantification_clusters_opti.py -> Quantification_clusters_opti.py (why opti ??? if useless remove it)